Export CBS_get_any_asn1_element.

Useful for parsing things when you don't know what tag to expect (e.g. a
CHOICE). Also allow its operands to be NULL, so that it can be used to skip
arbitrary elements.

Delete CBS_ASN1_ANY which wasn't doing anything.

Change-Id: I56413e68b4f2e13860ea3e55373d5830713d7e5c
Reviewed-on: https://boringssl-review.googlesource.com/1661
Reviewed-by: Adam Langley <agl@google.com>
diff --git a/include/openssl/bytestring.h b/include/openssl/bytestring.h
index a7507d8..6e18499 100644
--- a/include/openssl/bytestring.h
+++ b/include/openssl/bytestring.h
@@ -128,8 +128,6 @@
 #define CBS_ASN1_CONSTRUCTED 0x20
 #define CBS_ASN1_CONTEXT_SPECIFIC 0x80
 
-#define CBS_ASN1_ANY 0x10000
-
 /* CBS_get_asn1 sets |*out| to the contents of DER-encoded, ASN.1 element (not
  * including tag and length bytes) and advances |cbs| over it. The ASN.1
  * element must match |tag_value|. It returns one on success and zero
@@ -142,6 +140,18 @@
  * ASN.1 header bytes too. */
 OPENSSL_EXPORT int CBS_get_asn1_element(CBS *cbs, CBS *out, unsigned tag_value);
 
+/* CBS_get_any_asn1_element sets |*out| to contain the next ASN.1 element from
+ * |*cbs| (including header bytes) and advances |*cbs|. It sets |*out_tag| to
+ * the tag number and |*out_header_len| to the length of the ASN.1 header. If
+ * the element has indefinite length then |*out| will only contain the
+ * header. Each of |out|, |out_tag|, and |out_header_len| may be NULL to ignore
+ * the value.
+ *
+ * Tag numbers greater than 31 are not supported. */
+OPENSSL_EXPORT int CBS_get_any_asn1_element(CBS *cbs, CBS *out,
+                                            unsigned *out_tag,
+                                            size_t *out_header_len);
+
 /* CBS_get_asn1_uint64 gets an ASN.1 INTEGER from |cbs| using |CBS_get_asn1|
  * and sets |*out| to its value. It returns one on success and zero on error,
  * where error includes the integer being negative, or too large to represent